A project is proposed to develop reagents and methods for immobilizing receptors, including antibodies and Staphylococcal Protein A, onto membranes for affinity purifications, by photoimmobilizing hydrophilic polymeric coupling reagents to which the receptors will then be coupled. Reagents and methods are proposed to increase stability of the immobilized receptor or antibody molecules. The proposed approach is to synthesize hydrophilic polymers having photoactivatable groups and multiple groups that will react with antibodies or other receptors. The polymeric coupling reagents will be designed to form very open polymeric layers when immobilized to allow penetration of the receptors into the layer to achieve efficient coupling while also having very low nonspecific adsorption of proteins in the solutions being purified. The technology will be developed using model polyclonal antibodies after which it will also be and Staphylococcus aureus Protein A. Use of these methods for preparing affinity membranes is expected to increase the efficiency of the purification process, to improve the quality of such purified products and to reduce the costs of a variety of bioseparations, including purification of recombinant proteins, antibodies and plasma proteins from cell culture supernatants, plasma and ascites fluid.